Re: [OMPI users] shared memory zero size segment

No clarification necessary. Standard is not user guide. Semantics are clear from what is defined. Users who don't like the interface can write a library that does what they want. Jeff On Thursday, February 11, 2016, Nathan Hjelm wrote: > > I should also say that I think this

Re: [OMPI users] shared memory zero size segment

Indeed, I ran with MPICH. But I like OpenMPI's choice better here, which is why I said that I would explicitly set the pointer to bull when size is zero. Jeff On Thursday, February 11, 2016, Nathan Hjelm wrote: > > Jeff probably ran with MPICH. Open MPI's are consistent with

Re: [OMPI users] shared memory zero size segment

I should also say that I think this is something that may be worth clarifying in the standard. Either semantic is fine with me but there is no reason to change the behavior if it does not violate the standard. -Nathan On Thu, Feb 11, 2016 at 01:35:28PM -0700, Nathan Hjelm wrote: > > Jeff

Re: [OMPI users] shared memory zero size segment

Jeff probably ran with MPICH. Open MPI's are consistent with our choice of definition for size=0: query: me=1, them=0, size=0, disp=1, base=0x0 query: me=1, them=1, size=4, disp=1, base=0x1097e30f8 query: me=1, them=2, size=4, disp=1, base=0x1097e30fc query: me=1, them=3, size=4, disp=1,

Re: [OMPI users] shared memory zero size segment

You can be right semantically. But also the sentence "the first address in the memory segment of process i is consecutive with the last address in the memory segment of process i - 1" is not easy to interpret correctly for a zero size segment. There may be good reasons not to allocate the

Re: [OMPI users] shared memory zero size segment

Thanks Jeff, that was an interesting result. The pointers are here well defined, also for the zero size segment. However I can't reproduce your output. I still get null pointers (output below). (I tried both 1.8.5 and 1.10.2 versions) What could be the difference? Peter mpirun -np 4 a.out

Re: [OMPI users] shared memory zero size segment

See attached. Output below. Note that the base you get for ranks 0 and 1 is the same, so you need to use the fact that size=0 at rank=0 to know not to dereference that pointer and expect to be writing into rank 0's memory, since you will write into rank 1's. I would probably add "if (size==0)

Re: [OMPI users] shared memory zero size segment

On Thu, Feb 11, 2016 at 8:46 AM, Nathan Hjelm wrote: > > > On Thu, Feb 11, 2016 at 02:17:40PM +, Peter Wind wrote: > >I would add that the present situation is bound to give problems for some > >users. > >It is natural to divide an array in segments, each process

Re: [OMPI users] shared memory zero size segment

On Thu, Feb 11, 2016 at 02:17:40PM +, Peter Wind wrote: >I would add that the present situation is bound to give problems for some >users. >It is natural to divide an array in segments, each process treating its >own segment, but needing to read adjacent segments too. >

Re: [OMPI users] shared memory zero size segment

I would add that the present situation is bound to give problems for some users. It is natural to divide an array in segments, each process treating its own segment, but needing to read adjacent segments too. MPI_Win_allocate_shared seems to be designed for this. This will work fine as long

Re: [OMPI users] shared memory zero size segment

Yes, that is what I meant. Enclosed is a C example. The point is that the code would logically make sense for task 0, but since it asks for a segment of size=0, it only gets a null pointer, which cannot be used to access the shared parts. Peter - Original Message - > I think

Re: [OMPI users] shared memory zero size segment

I think Peter's point is that if - the windows uses contiguous memory *and* - all tasks knows how much memory was allocated by all other tasks in the window then it could/should be possible to get rid of MPI_Win_shared_query that is likely true if no task allocates zero byte. now, if a task

Re: [OMPI users] shared memory zero size segment

On Wed, Feb 10, 2016 at 8:44 AM, Peter Wind wrote: > I agree that in practice the best practice would be to use > Win_shared_query. > > Still I am confused by this part in the documentation: > "The allocated memory is contiguous across process ranks unless the info > key

Re: [OMPI users] shared memory zero size segment

I agree that in practice the best practice would be to use Win_shared_query. Still I am confused by this part in the documentation: "The allocated memory is contiguous across process ranks unless the info key alloc_shared_noncontig is specified. Contiguous across process ranks means that the

Re: [OMPI users] shared memory zero size segment

I don't know about bulletproof, but Win_shared_query is the *only* valid way to get the addresses of memory in other processes associated with a window. The default for Win_allocate_shared is contiguous memory, but it can and likely will be mapped differently into each process, in which case only

Re: [OMPI users] shared memory zero size segment

Peter, The bulletproof way is to use MPI_Win_shared_query after MPI_Win_allocate_shared. I do not know if current behavior is a bug or a feature... Cheers, Gilles On Wednesday, February 10, 2016, Peter Wind wrote: > Hi, > > Under fortran, MPI_Win_allocate_shared is called

Re: [OMPI users] shared memory zero size segment

Sorry for that, here is the attachement! Peter - Original Message - > Peter -- > > Somewhere along the way, your attachment got lost. Could you re-send? > > Thanks. > > > > On Feb 10, 2016, at 5:56 AM, Peter Wind wrote: > > > > Hi, > > > > Under fortran,

Re: [OMPI users] shared memory zero size segment

- Original Message - > Peter -- > > Somewhere along the way, your attachment got lost. Could you re-send? > > Thanks. > > > > On Feb 10, 2016, at 5:56 AM, Peter Wind wrote: > > > > Hi, > > > > Under fortran, MPI_Win_allocate_shared is called with a window size

Re: [OMPI users] shared memory zero size segment

Peter -- Somewhere along the way, your attachment got lost. Could you re-send? Thanks. > On Feb 10, 2016, at 5:56 AM, Peter Wind wrote: > > Hi, > > Under fortran, MPI_Win_allocate_shared is called with a window size of zero > for some processes. > The output pointer is

[OMPI users] shared memory zero size segment

Hi, Under fortran, MPI_Win_allocate_shared is called with a window size of zero for some processes. The output pointer is then not valid for these processes (null pointer). Did I understood this wrongly? shouldn't the pointers be contiguous, so that for a zero sized window, the pointer should